Geographic Influences on Emergency Laparotomy Outcomes

The aim of this study is to explore the possibility that outcomes from emergency laparotomy may vary according to:

• the urban-rural nature of the patient's home location and
• travel time from hospital.

This is a retrospective study of all emergency laparotomies performed in Scotland during the period from 1st January 2001 - 31st December 2010. It will use routinely collected administrative data from the Information Services Division (ISD) of NHS National Services Scotland.

Emergency laparotomy will be defined as a non-elective abdominal procedure primarily on the gut tube; and such cases will be identified by the use of a set of procedural codes, which will be validated against local records.

Potentially significant confounding variables such as age, gender, and co-morbidity will be studied for their predictive value in a univariate model and included in a multivariate model if they remain significant. The primary outcome measure will be risk-adjusted 30 day/inpatient mortality, and secondary outcome measures will be 30 day readmission rate, 30 day re-operation rate, and post-operative length of stay.

The registry which will supply the data for this study is the Scottish Morbidity Record 01 (SMR01), the full title of which is the "General / Acute Inpatient and Day Case dataset" (see http://www.adls.ac.uk/nhs-scotland/general-acute-inpatient-day-case-smr01/?detail). SMR01 is collated and administered by ISD, and data submission is mandatory for all Scottish NHS providers of in-patient or day-case care. Approximately 1.4 million records are added each year. Diagnoses are coded according to International Classification of Diseases (ICD)-10 standards and procedures are coded according to the United Kingdom's Office of Population Census Statistics (OPCS) standards, the most recent of which is version 4.5.

The data quality in SMR01 is high and is assured by regular internal audits. In the 2010 audit of accuracy, Main Condition was recorded with an accuracy of 88% and Main Procedure was recorded with an accuracy of 94%. Where data inconsistencies are identified in the extract supplied for this study, further clarification will be obtained where possible with ISD's data retrieval support team. Data completeness is very high in SMR01. However, where significant volumes of data are missing or unusable, the need for data imputation will be explored.

The study period was decided on pragmatically by a desire to provide an assessment of contemporary practice, fully within the era of wide-spread laparoscopic surgery.

A power calculation also suggested that this would provide an adequate sample size to demonstrate mortality differences. A recent paper showed 30 day mortality for emergency laparotomy to be 14.9% (Saunders DI, Murray D, Pichel AC, Varley S, Peden CJ. Variations in mortality after emergency laparotomy: the first report of the UK Emergency Laparotomy Network. Br J Anaesth. 2012 Sep 1;109(3):368-75.)

It was decided that we wanted to be able to detect a mortality difference (absolute) of 2%. Alpha was specified as 0.05 and power 0.9. Using a chi-2 test in G Power 3.1.7, it was determined that a total N of 5221 was required to show this difference. In the study already cited, 35 hospitals submitted data on 3 months of practice, giving a total of 1853 patients. We extrapolated to estimate that one hospital completes 212 laparotomies per year. There are currently 31 adult surgical centres in Scotland, resulting in an estimate of 6,565 laparotomies per year. Even accepting the smaller size of Scottish hospitals, this demonstrates that a 10 year cohort should be more than adequate to detect a clinically significant difference in length of stay.

The investigators will use the Scottish government's own 8-fold urban-rural classification system (see http://www.scotland.gov.uk/Topics/Statistics/About/Methodology/UrbanRuralClassification) to investigate the possible relationship between patient geographical location and outcome. Urban-rural categories may be grouped for analysis, according to initial exploratory work.

The investigators will further calculate the approximate travelling time from patient home location (using postcode) to the treating hospital, by constructing isocrones at time/distance intervals from hospitals. Travel time will be analysed as a continuous and discrete variable.

Inclusion criteria

• All patients aged 18 years or older who undergo emergency laparotomy within the study period

Exclusion criteria

• Patients who are non-resident in Scotland
• Multiple laparotomies on a single patient will not be counted as separate index events unless ≥6 months have passed between previous discharge and new hospital admission.